In case a van type truck is to have its bed loaded with freights in the prior art, there has been generally performed a loading method called "manual loading", in which the freights on a pallet are transported to the entrance of the bed by a fork lift and are manually conveyed and loaded on a predetermined position on the bed. This manual loading method is troublesome and requires a large amount of labor in moving the freights in the bed.
In order to facilitate the movement of freights in the bed of a truck, therefore, the truck bed is provided with a liftup conveyor, as disclosed in Japanese Patent Laid-Open No. 53907/1989. This liftup conveyor is equipped with free roller rows which can move up and down from a freight stacking face. When the freights are to be stacked and then moved on the bed, the free roller rows are lifted from the freight stacking face and the freights rolled on the free roller rows until they are loaded in a predetermined position in the bed. While the truck is running, on the other hand, the free roller rows are lowered from the freight stacking face so that the freights are stably placed without any slip on the freight stacking face. Specifically, this liftup conveyor is provided for lifting the free roller rows from the freight stacking face, when the freights are to be loaded or unloaded, to ensure the smooth conveyance of freights to facilitate the movement of freights in the bed.
If, however, this liftup conveyor is applied to the bed of a truck, the man power can be considerably spared, as compared with the manual loading, but the freights themselves have to be manually pushed in the truck bed at the freight loading/unloading time. Thus, there is left a problem that the freights cannot be automatically loaded/unloaded. Moreover, two or more operators are required for transporting the freights to the entrance of the bed by the fork lift at the loading time and for manually pushing the freights on the bed to roll them on the free roller rows. If these working operations are to be performed by a single operator, the operator has to push the freights by hand on the bed after he has driven the fork lift. Thus, there is left a problem that the loading operation of freights takes a long time and a large amount of labor.
As disclosed in Japanese Utility Model Laid-Open No. 41451/1989, therefore, there has been proposed a wide belt conveyor structure, in which a wide belt is arranged all over the surface of the freight stacking face of a truck bed so that it may be slipped on the freight stacking face by take-up means disposed at the front or rear portion of the to convey the freights sequentially forward on the belt.
If this wide belt conveyor is applied to the truck bed, the freights can be automatically moved in the bed after they have been transferred to the bed by the fork lift. However, the wide belt has to be moved while bearing the total weight of the freights, so that the belt receives a serious load to require large-scaled drive means. This large scale raises a problem that the system has its total weight and whole volume enlarged to reduce the carrying capacity accordingly. Still the worse, the weight of the freights is continuously applied while the truck is running, so that the belt is liable to wear.